1) Field of the Invention
The present invention relates to the art of separating free-flowing, non-ferromagnetic, conducting materials from non-ferromagnetic, nonconducting free-flowing materials, such materials being mixed together, by virtue of electrical conductivity, magnetic susceptibility and density.
The invention is particularly well suited for processing placer deposits of free-flowing auriferous metal(s) ores in the industry. Auriferous particles in placer geological deposits may be effectively and efficiently separated from the sand and gravels in which they naturally occur.
2) Description of the Prior Art
The methods of segregating non-ferromagnetic, conductive, free-flowing materials from non-ferromagnetic, nonconductive materials fall into one of three categories:
1. high tension
2. heavy media
3. eddy current
The present invention is of the eddy current type. It is common knowledge that a time varying magnetic field will induce electrical currents in conducting materials within the influence of such magnetic fields. It is also known that if a magnetic field moves with respect to an electrically conductive body, or vice versa, electrical currents are induced in a conducting body. In the latter case, the eddy currents induced in the conducting body and their interaction with the magnetic field that produced them, produce forces which accelerate the conducting body in the direction of the moving magnetic field.
A prior art method and apparatus is exemplified in U.S. Pat. No. 4,003,830. The separation apparatus comprises a planar area array of permanent magnets arranged to form alternating strips of north and south polarity. The material to be processed is caused to slide down an incline plane over the planar array of magnets such that the conductive particles in said material will have induced electrical currents flowing within them and the attendant electromagnetic forces cause the conducting particles to be separated from the nonconductive particles.
Another method of the prior art is exemplified in U.S. Pat. No 4,238,323. According to this method, the flow of material to be processed is caused to free-fall into a region of space permeated by a non-uniform magnetic field. The non-uniform magnetic field is created by a magnetic circuit composed of a "C" shaped ferromagnetic pale piece with a beveled surface on each pale piece face. Non-ferromagnetic material, comprised of both conductive and nonconductive material, is caused to free-fall into the region of space between the above pole pieces. Eddy currents are induced in the conducting particles as in similar methods and such currents interact with the magnetic field generated by the above magnet such that the conducting particles move from the region of highest field intensity to lowest field intensity. The free-fall trajectory of the nonconducting particles is unaffected by the presence of the magnetic field.
Both of the above inventions are not particularly well suited for the processing of auriferous materials because neither apparatus is capable of processing sufficiently large volumes of material for a substantial profit. The apparatus described in U.S. Pat. No. 4,003,830 utilizes permanent magnets. Such magnets are adequate for the separation of light metals of the non-ferromagnetic type, such as aluminum, from municipal waste. However, such an apparatus utilizes permanent magnets which are far less powerful than electromagnets and therefore cannot generate sufficient field strength to extend sufficiently far from the surface of the inclined plane to permit the processing of large volumes of material. Furthermore, said apparatus in U.S. Pat. No. 4,003,830 would have severe maintenance problems associated with the abrasive destruction of the inclined plane surface over which the auriferous material would flow. Further still, the inclined plane of the above apparatus intrinsically is a lower throughput device than a free-fall device. The apparatus described in U.S. Pat. No. 4,238,323 utilizes electromagnets which are capable of extending a considerable distance from one pole to the other. However, said apparatus relies upon the relatively narrow volume of space permeated by the region of high magnetic field intensity. Again the result is an apparatus which is capable of processing only laboratory scale volumes of material. In a typical mining operation, the above apparatus would not be practical. Furthermore, were the above apparatus to be scaled up in size, it would consume large amounts of power to effect separation of an impractically small amount of material.